Many electronic products need various amounts of memory to store information, e.g. data. One common type of high speed, low cost memory includes dynamic random access memory (DRAM) comprised of individual DRAM cells arranged in arrays. DRAM cells include an access transistor, e.g. a metal oxide semiconducting field effect transistor (MOSFET), coupled to a capacitor cell.
Another type of high speed, low cost memory includes floating gate memory cells. A conventional horizontal floating gate transistor structure includes a source region and a drain region separated by a channel region in a horizontal substrate. A floating gate is separated by a thin tunnel gate oxide. The structure is programmed by storing a charge on the floating gate. A control gate is separated from the floating gate by an intergate dielectric. A charge stored on the floating gate effects the conductivity of the cell when a read voltage potential is applied to the control gate. The state of cell can thus be determined by sensing a change in the device conductivity between the programmed and un-programmed states.
With successive generations of DRAM chips, an emphasis continues to be placed on increasing array density and maximizing chip real estate while minimizing the cost of manufacture. It is further desirable to increase array density with little or no modification of the DRAM optimized process flow.
Flash memories based on electron trapping are well known and commonly used electronic components. Recently NAND flash memory cells have become common in applications requiring high storage density while NOR flash memory cells are used in applications requiring high access and read speeds. NAND flash memories have a higher density because 16 or more devices are placed in series, this increases density at the expense of speed.
Thus, there is an ongoing need for improved DRAM technology compatible flash memory cells. It is desirable that such flash memory cells be fabricated on a DRAM chip with little or no modification of the DRAM process flow. It is further desirable that such flash cells provide increased density and high access and read speeds.